It is often useful to determine properties of various rock formations, such as to determine the porosity, permeability, and/or composition of rock formations. For example, it is desirable to determine properties of rock formations encountered during drilling of hydrocarbon exploration and production wells so as to provide information with respect to the ability of the rock formations to store hydrocarbon reserves and/or the ability of the rock formations to allow fluids to flow through them. To optimize well completion strategies, the lithology and mineralogy of the rock formations are important.
In all rocks the physical strength of the rock is related to the minerals found in the rock, the pore structure, and the cementation of the rock. In fine grained clastic rocks, such as conglomerate, sandstone, siltstone, and shale, the sealing capacity of the rock is related to silt content, wherein the sealing capacity parameter (e.g., capillary entry pressure) controls whether the rock can hold a hydrocarbon column below it now or in the geological past. Parameters such as fraccability are related to silt or quartz content of fine grained siliciclastic rocks. Accordingly, well fracturing strategies for tight shale gas may be limited to particular mineralogies, such as rock formation zones with high quartz content, in order to deliver more effective fracture length.
To determine various rock properties, quantitative mineralogical compositions of rock samples are often needed. For example, quantitative X-Ray diffraction techniques may be utilized with respect to rock samples to determine mineralogy. However, such analysis is generally relatively expensive and often time-consuming, requiring on the order of days or weeks to complete the analysis. Conventional or sidewall core samples are traditionally needed to determine some rock properties, such as rock porosity and permeability. Such samples are costly and often it is not possible to obtain core samples, such as where a lack of well bore stability does not permit the removal of the drill string for insertion of a core sample collection tool. Using such core samples, when available, porosity and permeability may be determined in specialized laboratories through application of confining stresses in costly and time consuming procedures.
It is possible to measure, often indirectly, some rock properties using well-logging tools, such as wireline logging tools. However, running such logging tools is expensive, time consuming and sometimes not possible, such as due to well bore instability.
It can be appreciated from the foregoing that the presently available techniques for determining various properties of rock formations are generally expensive and time-consuming. Moreover, irrespective of cost and time required to make the determinations, many such techniques are often not available in particular situations.